Our overall objectives are to improve on methods of detection, monitoring and treatment of respiratory insufficiency which may follow anesthesia, surgery or trauma. Capacitance respirometry will be evaluated as a continuous monitor for spontaneously breathing patients with respiratory insufficiency. Patients with head injuries or following cranial surgery will also be studied in conjunction with blood gas studies, since little is known about the origins of respiratory insufficiency in this group of patients. Continuous blood gas analysis will be done during induction of anesthesia and during surgery involving cardiopulmonary bypass to determine the clinical advantages of the technique, if any, over intermittant blood sampling. Patients with intrapulmonary shunts greater than 20-30 percent that have been refractory to changes in ventilatory assistance, often are treated with inspired oxygen concentrations (FI02) greater than 50-60 percent. A third objective of our research is to obtain laboratory and clinical data to establish guidelines for the use of safe concentrations of inspired oxygen in the presence of significant shunting. Changes in FI02 will be assessed in relation to changes in arterial and mixed venous oxygen tensions, cardiac output, oxygen delivery and oxygen reserve.